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By Jonathan Hale
As you may remember from last year, April may be baseball season but it’s not always baseball weather. At the beginning of 2007, several games (including the Chicago White Sox home opener) were postponed due to frigid conditions and harsh winds. From frozen fingers on the mound to painful vibrations at bat, I doubt anyone likes playing in cold weather. But does the advantage shift towards either hitters or pitchers as the thermometer rises throughout the year? Pitch f/x includes a record of the temperature for each game, so let’s take a look at the big three of batting average, on-base percentage and slugging percentage.
Not only do hitters have a very hard time in the coldest of weather, there is a steady climb from the worst numbers in the bitter cold up to the low 80’s, where results level off. And the swing is significant- batters in weather under 50 degrees Fahrenheit average .249/.318/.410 while in a pleasant 81-85, they hit .297/.356/.468.
I’m sure some of you have caught on to the fact that this could be putting the cart before the horse – maybe hitters are just catching up to pitchers as the year goes on and they shake off the rust of a long off-season, and temperatures just happen to be going up at the same time during the hot summer months. While that’s possible that has an effect as well, except for a very poor April, last year hitters didn’t do any better as the season went on:
Month
| Average Temp
| AVG
| OBP
| SLG
| April
| 60
| .255
| .327
| .404
| May
| 68
| .273
| .341
| .430
| June
| 73
| .276
| .342
| .422
| July
| 75
| .272
| .336
| .423
| August
| 78
| .273
| .336
| .429
| September
| 74
| .274
| .343
| .427
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That’s where this data comes from, so while the very low sub-50 numbers could be due to rust, the gradual increase in offence really can be traced back to the temperature, and not just the date on the calendar. Frozen Shots
As you can see from the first graph, while in very cold temperatures hitters have their worst average and on-base percentage, slugging averages don’t suffer as much. Here’s one reason why- a lot of home runs come in the worst of weather, and from there on it’s the steady climb as seen in the rest of the stats.  Again, this could be because some pitchers don’t have a feel for some of their pitches out of the gate and are hanging breaking balls (or something), but home run rates are out of line with the rest of the results. Pitch Breakdown
Unfortunately, I don’t have any confidence in my pitch identification for pitches like 2-seamers and changeups that are pretty close to each other, but it’s pretty easy to isolate 4-seam fastballs and big breaking balls as I’ve done in previous articles. One thing that really stands out as the weather gets warmer is the vertical movement on these two pitches. 4-Seam Fastball
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As the temperature rises, 4-seam fastballs rise less and less (although their velocity does not change), and the total swing is an inch of movement. “Rise” on a pitch is due to backspin, so maybe that’s a factor of humidity/sweat giving a pitcher less grip? Whatever the cause, losing that movement can’t be good for a power pitcher.
Curveballs on the other hand don’t have as much bite on them in warmer weather- this time the total difference is just less than an inch in drop.
Less movement on pitches is just one possible reasons for why hitters have the advantage in warmer weather- it could equally well be a matter of control or that it’s easier to hit in temperate conditions. But one thing is clear- the next time you see a pitcher blowing on his hands and shivering on the mound, don’t feel so bad for him. It could be a beautiful day, and then he’d really be uncomfortable.
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